The molecule pictured below is acrylonitrile, the building...

The molecule pictured below is acrylonitrile, the building block of the synthetic fiber Orlon.
(a) Which is the shorter carbon-carbon bond?
(b) Which is the stronger carbon-carbon bond?
(c) Which is the most polar bond and what is the partial negative end of the bond?

Key Concepts

Electronegativity and Bond Polarity

Electronegativity describes an atom’s tendency to attract shared electrons in a chemical bond. When atoms with different electronegativities are bonded, the electron density shifts toward the more electronegative atom, creating a polar bond with partial charges. Understanding this principle helps explain why bonds like the carbon–nitrogen bond (within a nitrile group) are quite polar, with the nitrogen bearing the partial negative charge.

Conjugation and Resonance Effects

Conjugation involves the overlap of p-orbitals across adjacent bonds, allowing electrons to be delocalized over multiple atoms. This electron delocalization can modify bond orders and therefore influence bond lengths and strengths. In molecules with alternating single and multiple bonds, conjugation may impart partial multiple-bond character to bonds that are nominally single, affecting their physical properties.

Bond Order

Bond order is a measure of the number of chemical bonds between a pair of atoms. Generally, bonds with a higher bond order (such as double or triple bonds) are shorter and stronger than those with a lower bond order (such as single bonds). This concept is crucial when comparing carbon?carbon bonds because variations in the number of shared electron pairs lead to measurable differences in bond lengths and strengths.

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